1. Field of the Invention
This invention generally relates to an electrical apparatus provided with a counter for counting the number of specific operations of the apparatus, and more particularly, to an electrical apparatus designed to prevent unauthorized use of the electrical apparatus.
2. Description of Related Art
When a copying apparatus is lent to a user, a copying fee is charged based on the number of copies counted by a counter installed in the copying apparatus. Therefore, if the counter is detached from the copying apparatus during copying, it is impossible to correctly know the number of copies made and to collect a correct copying fee.
Therefore, conventionally, such a device as indicated in FIG. 1 is mounted to the copying apparatus to prevent unauthorized use of the copying apparatus. A main body 1 of the copying apparatus has counter connecting terminals 1a, 1b, 1c, 1d. The counter connecting terminal 1a is earthed. The counter connecting terminal 1b is connected to a power source V1 through a resistance R11 and also to an input port a of a CPU 2. The counter connecting terminal 1c is connected to a power source V2 whose voltage is higher than that of the power source V1. An output port b of the CPU 2 is connected to a power source V3 through a resistance R12 and to the counter connecting terminal 1d through an open-collector circuit 3. The counter connecting terminals 1c, 1d are connected both to a power terminal 4c of a counter 4 and to an actuating signal terminal 4d which supplies the actuating signal to the counter 4, through a connector CN. The counter 4 is started by the actuating signal. A counter relay CR is connected between the power terminal 4c and an actuating signal terminal 4d. An appropriate signal at activating signal terminal will increment the value of the counter 4.
In the case where the counter 4 is connected to a copying apparatus, since the counter connecting terminals 1a, 1b are short-circuited by a short circuit S therebetween, the input port a of the CPU 2 is at the "L" level. In this state, the CPU 2 is enabled to output an instruction (not shown) to start copying. Therefore, an actuating signal at the "L" level is output from the output port b of the CPU 2 to the open-collector circuit 3 to count a copy operation. This allows a current flow from the power source V2 to the open-collector circuit 3 through the counter relay CR, whereby the counting value of the counter 4 is increased one. The increased value is displayed.
Meanwhile, if the counter 4 is detached from the copying apparatus by separating the connector CN the voltage of the counter connecting terminal 1b is raised to that of the power source V1 and the input port a of the CPU 2 goes to the "H" level. The CPU 2 detects that the counter 4 is detached and prohibits generation of a copy instruction signal thereby making copying impossible.
In the manner as described hereinabove, unauthorized use of the copying apparatus has been prevented, and a correct counting of the number of copies made has been recorded by the counter.
In the aforementioned approach, however, if the counter connecting terminal 1c and power terminal 4c and, counter connecting terminal 1d and actuating signal terminal 4d are separated from each other at a position, for example, indicated by the broken line 5 in FIG. 1, the counter 4 will not function. Since the counter connecting terminals 1a, 1b are kept in the short-circuited state by the short circuit S of the counter 4, and the input port a of the CPU 2 is at the "L" level, generation of a copy instruction signal is not prohibited by the CPU 2. In such case as above, the counting value of the counter 4 is never updated even when copying is continued, resulting in the improper use of the counter.